The Autonomic Nervous System

The Autonomic Nervous System

Assess Prof. Fawzia Al-Rouq

Department of Physiology

College of Medicine

King Saud University

Autonomic Nervous System

LECTUR (1)

Functional Anatomy &

Physiology of

Autonomic NS

INTRODUCTION

THE NERVOUS SYSTEM

•The nervous system monitors and controls almost every organ / system through a series of positive and negative

feedback loops.•The Central Nervous System (CNS): Includes the brain

and spinal cord. •The Peripheral Nervous System (PNS): Formed by

neurons & their process present in all the regions of the body.

•It consists of cranial nerves arises from the brain & spinal nerves arising from the spinal cord.

•The peripheral NS is divided into •Somatic Nervous system

•Autonomic nervous system

The Autonomic Nervous System

OBJECTIVES

• Anatomy and physiology of Autonomic Nervous System

• At the end of this lectutre (1)the student should be able to:-

• -appreciate the anatomy of symathetic& parasympathetic nervous system.

• -explain physiological functions of Symathetic &parasympathetic nerves in head&neck,chest,abdomen and pelvis

FUNCTIONAL ANATOMY OF THE

AUTONOMIC NERVOUS SYSTEM

The Autonomic Nervous System

• ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control

• Visceral motor innervates non-skeletal (non-somatic) muscles

• Composed of a special group of neurons serving: – Cardiac muscle (the heart)– Smooth muscle (walls of viscera and blood vessels)– Internal organs– Skin

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Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system

Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system

• Somatic division:– Cell bodies of motor neurons reside in CNS (brain

or spinal cord)– Their axons (sheathed in spinal nerves) extend all

the way to their skeletal muscles• Autonomic system: chains of two motor

neurons– 1st = preganglionic neuron (in brain or cord)– 2nd = ganglionic neuron (cell body in ganglion

outside CNS)– Slower because lightly or unmyelinated 12

• Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron

• Axon of 2nd (ganglionic) neuron extends to the organ it serves

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this dorsal root ganglion

is sensory

Sympathetic Innervation of Visceral Targets

• Ganglia close to spinal cord

• Short, lightly myelinated preganglionic neurons

• Long, unmyelinated postganglionic neurons

Spinal

Cord

Parasympathetic Innervation of Visceral Targets• Ganglia close to or on target organs

• Preganglionic neurons - long

• Post ganglionic neurons - short

SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEM ORIGIN

Blue= Para symp; Red symp

Sympathetic - Origin• Thoracolumbar lateral horns of the spinal segments T1-L2.

• Nerve fibers originate between T1 & L2

Parasympathetic - OriginCraniosacral Cell bodies of the motor nuclei of the cranial nerves III, VII,

IX and X in the brain stem Second, third and fourth [S2-S4] sacral segments of the spinal cord

• Nerve fibers emerge from brain & • sacrum cranio-sacral outflow

PARASYMPATHETIC NERVOUS SYSTEM

The cranial nerves III, VII and IX affect the pupil and salivary gland secretion

Vagus nerve (X) carries fibres to the heart, lungs, stomach, upper intestine and ureter

The sacral fibres form pelvic plexuses which innervate the distal colon, rectum, bladder and

reproductive organs.

PHYSIOLOGICAL FUNCTIONS OF THE

AUTONOMIC NERVOUS SYSTEM

SYMPATHETIC NERVOUS SYSTEM FUNCTIONS

The sympathetic system enables the body to be prepared for fear, flight or fight

Sympathetic responses include an increase in heart rate, blood pressure and cardiac output Diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal

muscle Increased pupil size, bronchiolar dilation,

contraction of sphincters and metabolic changes such as the mobilisation of fat and glycogen.

FEAR, FLIGHT OR FIGHT

FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM

Bronchioles dilate, which allows for greater alveolar oxygen exchange.

It increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a

mechanism for the enhanced blood flow to skeletal muscles.

Sympathetic nerves dilate the pupil and relax the lens, allowing more light to enter the eye.

PARASYMPATHETIC NERVOUS SYSTEM FUNCTIONS

The parasympathetic nervous system has "rest and digest" activity.

In physiological terms, the parasympathetic system is concerned with conservation and restoration of energy, as it causes a reduction in heart rate and blood pressure, and

facilitates digestion and absorption of nutrients, and consequently the excretion of waste products

PHYSIOLOGICAL FUNCTIONS OF THE

AUTONOMIC NERVOUS SYSTEM

The Autonomic Nervous System

Structure

Sympathetic Stimulation Parasympathetic Stimulation

Iris (eye muscle)

Pupil dilation Pupil constriction

Salivary Glands

Saliva production reduced

Saliva production increased

Oral/nasal Mucosa

Mucus production reduced

Mucus production increased

HeartHeart rate and force increased

Heart rate and force decreased

LungBronchial muscle relaxed

Bronchial muscle contracted

The Autonomic Nervous System

Structure Sympathetic Stimulation Parasympathetic Stimulation

Stomach Peristalsis reducedGastric juice secreted; motility increased

Small Intes

Motility reduced Digestion increased

Large Intes

Motility reduced Secretions and motility increased

LiverIncreased conversion ofglycogen to glucose

Kidney Decreased urine secretion Increased urine secretion

Adrenal medulla

Norepinephrine andepinephrine secreted

BladderWall relaxedSphincter closed

Wall contractedSphincter relaxed

Subdivision

Nerves Employed

Location of Ganglia

Chemical Messenger

General Function

Sympathetic

Thoracolumbar

Alongside vertebral column

Norepinephrine

Fight or flight

Parasympathetic

Craniosacral On or near an effector organ

Acetylcholine

Conservation of body energy

THE AUTONOMIC

NERVOUS SYSTEM

LECTUR (2)

MECHANISM OF ACTIONS

The neurotransmitters & receptors of Autonomic NS

OBJECTIVES

OBJECTIVES• At the end of this lecture (2)the

student should be able to:-

• describe neurotransmitters that can release at pre and post ganglionic of Autonomic NS.

• Describe Autonomic NS receptors.

ANS Neurotransmitters:  Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released

Adrenergic

Cholinergic

Sympathetic Neurotransmitters• Preganglionic neurons - • Cholinergic = ( release acetylcholine ) • Postganglionic neurons:

release norepinepherine at target organs ie. Adrenergic – except sweat glands & bl vessels to skeletal muscles

Parasympathetic Neurotransmitters

• Pre & Postganglionic neurons release acetylcholine = Cholinergic

Chemical or neural transmitter

• All preganglionic fibers release acetylcholine (Ach).

• All parasympathetic postganglionic release Ach.

• All sympathetic postganglionic release noradrenalin except sweat glands & bl vessels to skeletal muscles

Autonomic Nervous system Receptors

Sympathetic Adrenergic Receptors

Parasympathetic cholinergic Receptors

Adrenergic Receptors are either Alpha or Beta • Alpha (α) adrenergic receptors are found in :

– Iris– Blood vessels– GIT

• Beta (β) adrenergic receptors can be beta one (β1) or beta 2 (β1) found in :

– Heart (β1)Bronchioles (β2)– Skeletal muscle (β2) – GIT (β2)

• Norepinephrine mainly excite α (and β to a lesser extent)

• Epinephrine excites both α & β equally

Adrenergic receptors blockers • α blockers:

Prazosin (α 1)Yohimbine (α 2)

• β blockers:Propranolol (β1 & β2)Atenolol (β 1)

Cholinergic Receptors

Cholinergic Receptors•Are divided into•)1 (Nicotinic found in all ganglia ( i.e., the

synapses between pre- & postganglionic of both sympathetic & parasympathetic divisions of the ANS

•)2 (Muscarinic found on all effector cells innervated ( & stimulated ) by

•)1 (postganglionic parasympathetic fibers & , •)2 (postganglionic cholinergic sympathetic nerves

(blood vessels of skeletal muscles & sweet glands)

Drugs block cholinergic receptors:Hexamethonium (block both types)Atropine (block muscarinic receptors)